This invention relates to a gas fired direct contact water heater.
More particularly the invention concerns a gas fired water heater of the type (hereinafter called the type referred to) comprising gas burner means, a flow path for hot products of combustion from said burner means, water supply means to supply water to flow along said flow path in an opposite direction to the simultaneous flow of said products of combustion therealong and wherein heat from said products of combustion becomes transferred to the water which becomes heated thereby, and conduit means to convey said heated water subsequent to it travelling along said flowpath.
One known mode of use of water heaters of the type referred to is to mount the heater in an elevated position to ensure that the heated water output in the conduit means has an adequate head of pressure for the water user's needs when a user controlled valve connected to the conduit means is opened. The need to mount the heater in an elevated position can be a disadvantage because such a position is not always available. Furthermore it can make access to the heater difficult.
In another known mode of use, a pump and a flow detector are included in the conduit means. When the user controlled valve is opened the flow detector observes the slight, low pressure flow of water along the conduit means to meet the demand. In response the flow detector sends a signal to pump control means causing the latter to operate the pump to deliver the water output to the user. When the user's valve is closed, the water flow along the conduit means stops. This is observed by the flow detector which causes the pump control means to stop the pump. One disadvantage of this system is that there is a time delay caused by having to start up the pump and allow it to reach its steady operating state before the water output is at a desired pressure.
In both the aforesaid modes, when there is no demand for water output gas supply to the burner means is automatically turned off. But opening of the user's valve has the effect of causing heater control means to ignite the gas burner means to heat water which is now flowing along the flow path for supply to the user. However, in the interests of safe operation of gas fired apparatus and to meet legal requirements, the control means does not ignite the burner means immediately. Instead the control means causes a stream of purging air to be initially sent through a combustion chamber associated with the burner means for a predetermined period, for example about thirty seconds, before the control means causes the burner means to be ignited. Such a delay in ignition frequently means the occurence of the disadvantage that there is a very noticeable delay before the water being delivered to the user reaches a desired pre-determined elevated temperature.
An object of this invention is the provision of a water heater of the type referred to capable of being constructed to avoid or at least mitigate the aforesaid disadvantages.